Renal artery stenosis – causes, symptoms, diagnosis, treatment, pathology

Renal artery stenosis – causes, symptoms, diagnosis, treatment, pathology


With renal artery stenosis, ‘stenosis’
means narrowing, which refers to a progressive narrowing of the renal artery, which carries
blood to the kidney. This means that the blood downstream of the
narrowed spot that goes to the kidney is at lower pressure, which gets sensed by the kidney. Since an important role of the kidney is to
sense and help the maintain a normal blood pressure, the kidney then tries to raise blood
pressure throughout the body. Inside the kidney, there are millions of nephrons,
each of which help to filter the blood and then fine-tune the composition of blood by
carefully reabsorbing and secreting electrolytes as fluid passes through various parts of the
nephron. Blood approaches the nephron via the afferent
arteriole. You can remember it as ‘A’ for approach,
and then forms a tangle of capillaries called the glomerulus, before exiting via the efferent
arteriole – “e” for exit. That efferent arteriole goes on to split into
another set of capillaries – the vasa recta – which surround the nephron, and then blood
leaves via the venule. So there are two capillary beds per nephron,
usually we think of it going arteriole – capillary – venule, but in the nephron it goes arteriole
– capillary – arteriole – capillary – and finally venule. So nephrons have the general shape of the
letter “U”, with the beginning and end portions getting pretty close to each other. The reason that this matters, is that over
here, lining the inside of the afferent arteriole are endothelial cells. Wrapped around them are juxtaglomerular cells
which are super special smooth muscle cells that contract down like normal smooth muscle
cells, but also have the ability to release a hormone called renin in response to low
blood pressure. Over here, close to the distal convoluted
tubule, there is another special group of cells that line the tubule called macula densa
cells which are sodium-chloride-sensing cells that detect the sodium concentration in the
tubule. These two clusters of cells work together
because if the blood pressure falls, less blood is filtered and less sodium gets into
the tubule. This is then detected by the macula densa
cells and they send out a local prostaglandin signal that reaches the juxtaglomerular cells
and causes them to release renin. In addition the juxtaglomerular cells are
able to directly sense low pressure in the afferent arteriole, and also respond to sympathetic
nerve fibers to release renin. Now, renin helps to constrict blood vessels
and increases sodium reabsorption in the nephrons, which ultimately causes blood pressure to
rise. Normally, as the blood pressure rises, the
juxtaglomerular cells are no longer triggered to release renin, so balance is restored. One cause of renal artery stenosis is atherosclerotic
plaque buildup, which is where a mix of fat, calcium, and immune cells form a crusty rim
on the inside of the artery. Another cause, though, is renal fibromuscular
dysplasia, where fibro- refers to fibrous collagen connective tissue, -muscular refers
to smooth muscle in the artery wall, and -dysplasia means abnormal development. So, renal fibromuscular dysplasia is when
something goes wrong with connective tissue and smooth muscles in the walls of renal artery,
resulting in a series of bulges and narrow spots that leaves the artery looking like
a “string of beads” instead of a uniform cylinder. Fibromuscular dysplasia classically develops
in young women, but the exact underlying cause is still unclear. In both atherosclerosis and renal fibromuscular
dysplasia, the renal artery narrows and that causes the blood pressure to stay low in the
kidney as well as all the kidney’s nephrons. As a result, the juxtaglomerular cells release
renin, which might raise the blood pressure in the body and vessels before the stenosis,
but the pressure in the kidney and the afferent arterioles stays low, so they just keep releasing
renin. So renal artery stenosis creates a vicious
cycle of high blood pressure, or hypertension, which puts incredible stress on the blood
vessels and can contribute to having a stroke or heart attack. Also, since the affected kidney receives less
blood than usual, it eventually starts to atrophy or shrink in size, as the kidney cells
die off and get replaced by fibrotic scar tissue. If the renal artery stenosis involves only
one of the kidneys, then the other kidney can often pick up the slack. But if both kidneys are affected, then it
can lead to acute kidney injury or acute renal failure. Symptoms are often a result of the hypertension,
which if it becomes severe, it can cause symptoms like headaches and blurry vision. The diagnosis is therefore based on seeing
if there’s an underlying cause for hypertension. Physical examination might reveal a bruit
– which is a whooshing sound heard with a stethoscope over the renal arteries in the
abdomen caused by the turbulence of blood flowing through the stenotic part of the renal
artery. Basic screening labs like serum creatinine
and a urinalysis can help assess kidney function as well, and imaging studies like ultrasound,
CT, and MRI can visualize the kidney. For example, in this CT scan of the abdomen,
the atrophied kidney is a lot smaller than the healthy one on the other side. Ultimately, since the problem is in the renal
artery, a renal arteriography can be done to visualize the renal artery with dye, to
see if there’s evidence of a blockage. Generally atherosclerosis forms in the beginning
portion of the renal artery where it branches from the aorta, whereas fibromuscular dysplasia
develops in the middle to far end of the renal artery, nearest to the kidney. Treatment of renal artery stenosis is aimed
largely at trying to manage hypertension, through using medications, as well as adopting
healthy eating and exercising habits. In addition, a surgical procedure called balloon
angioplasty can sometimes be used – and this is where a balloon is used to open up the
narrowed portions of the renal artery and, in rare cases, a tiny stent is left behind
to keep the artery propped open. An alternative option is to simply bypass
the stenosis with another artery that is grafted into place. Ultimately, if one kidney becomes atrophied
and nonfunctional, it also might be necessary to remove it. All right, as a quick recap. Renal artery stenosis is where the artery
that carries blood to the kidney becomes more narrow, which reduces the amount of blood
that the kidney receives as well as the blood pressure. The kidney senses the low blood pressure and
responds by releasing the hormone renin which increases blood pressure – ultimately causing
hypertension. Over time the lack of blood can also cause
the affected kidney to atrophy. Thanks for watching, you can help support
us by donating on patreon, or subscribing to our channel, or telling your friends about
us on social media.

47 Replies to “Renal artery stenosis – causes, symptoms, diagnosis, treatment, pathology”

  1. didn't need this video for my studies but I watched it anywayyy.. it's just so well explained and looks awesome!

  2. Really easy to follow along and learn. Lol at the kidney's many expressions. Thanks alot helped a great deal.

  3. By the way do you guys have any affiliation with www.passmedicine.com ? I tend to see your video links on their website.

  4. I have a question regarding RAS. Will a Renal Denervation procedure lower down the blood pressure because of lessening the release of renin by the kidney? And if yes, are there any solution/s to permanently treat the narrowing of the renal artery? Or still will go through life treatement?

  5. This is my favorite you tube channel! Re: pronunciation- is bruit not "Broo-ee"? I had never heard "Broot" before.

  6. Failed to mention that the imaging modalities covered don't reveal the haemodynamic significance of renal artery stenosis–which is necessary since renal artery stenosis and hypotension do not indicate renovascular hypertension. Also no mention of captopril renal scintigraphy?

  7. Hi, can u explain this topic a bit more like what happens in conc of renin angioteneion snd aldosterone in left n right veins in case of either of left n right artey stenosis ??

  8. Does it really only vasoconstrict before the stenosis? How does it cause vasoconstriction everywhere but not that one particular segment of the renal arteries?

  9. I don’t know how I just stumbled upon this, but wow, I’ve had a renal stenosis, I was born withOUT an Inferior Vena Cava. They tried to auto transplant my right kidney, but no such luck. They removed it, as well as did a few bowel resections. Could you do a video on “Collateral Circulation “? Cheers! Great work!

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